1. Field of the Invention
The present invention relates generally to a well drilling unit employed in prospecting for gaseous and liquid minerals, and more particularly but not by limitation, to and improved pipe wiper assembly for a well drilling unit.
2. Description of Prior Art
Well drilling units are employed in prospecting for gaseous and liquid minerals and for bringing them to the surface. Because of the need for drilling to greater depths, as well as improving the speed of the drilling operation, traditional precision drilling techniques have been superseded by continuous rotary drilling. Rotary drilling utilizes rotational motion of a bit to drill the well bore. The bit is attached to a drill string which is comprised of drill collars, drill pipe and a kelly joint. At the surface, rotational motion is imparted on the drill string by a rotary table to which the kelly joint is attached.
The drill cuttings produced by the bit operating at the bottom of the well bore are carried to the earth's surface by circulating drilling fluids, i.e. drilling mud. That is, the drilling fluids are continuously pumped down the well bore through the kelly joint, the drill pipe and the bit and recirculated to the surface.
As drilling progresses, new joints of drill pipe are added. This process is commonly known in the art as "making a connection". Conversely, the drill string must also be removed periodically to replace worn bits and damaged drill pipe. This process in commonly known in the art as "tripping out". Tripping out is performed by removing two to four joints of drill pipe at a time, depending upon the size of the derrick of the well drilling unit.
A consequence of tripping out is spillage of drilling fluids because as the drill pipe is removed from the well bore drilling fluids drain from the inside and outside of the drill pipe. The spillage results in drilling fluids being wasted and rig workers being exposed to unsafe working conditions.
To prevent fluid drainage from the drill pipe during tripping out, pipe wipers have herefore been utilized to wipe the outside surface of the drill pipe as the drill pipe is hoisted out of the well bore. However, when employing the housing assemblies of the prior art to support the pipe wipers problems have been encountered in that the drilling fluids are not uniformly removed from the outside surface of the drill pipe. For example, when the shims are removed from the rotary table in order to allow tripping out of the drill pipe the drill pipe can vertically move or sway which results in uneven wiping of the external surface of the drill pipe, as well as causing excessive wear on the pipe wipers.
Thus, a need has long existed for an improved fluid wiper assembly which could compensate for vertical deviations of the drill pipe during tripping out (and thereby enhance removal of the drill fluids from the external surface of the drill pipe), as well as improve the life of the pipe wipers. It is to such an improved fluid wiper assembly that the present invention is directed.